[Segawa disease].

Segawa disease (hereditary progressive dystonia with marked diurnal fluctuation) is an autosomal dominant, childhood onset, postural dystonia and the first hereditary basal ganglia disorder whose causative enzyme and gene defect were clarified. The initial symptom is unilateral pes equinovarus with marked diurnal fluctuation. Progression becomes slower after mid-teens and stationary after thirties. Postural tremor may occur after 10 years of age, especially after thirties. Parkinsonian resting tremor action and torsion dystonia. and disturbed locomotion do not occur. L-Dopa shows marked and sustained effect without side effects. F-Dopa PET and [11C] raclopride PET of over 20-year-old cases are normal. Deficiency of GTP cyclohydrolase I (GCH-I) was suggested from low CSF biopterin and neopterin. Mutation of GCH-I gene and decreased GCH-I were clarified as etiology. Twenty-five mutations discordant among families have been found. Autopsy of a gene proven case revealed decreased striatal tyrosine hydroxylase (TH) and dopamine (DA) in ventral striatum where direct pathway is predominant. Decreased GCH-I causes decreased tetrahydrobiopterin (BH4), TH and DA in nigrostriatal (NS) terminal. The lowest affinity of BH4 to TH causes selective involvement of DA. Postural dystonia is caused by decreased TH and DA affecting D1-direct pathway. Thalamic ventrolateral and pedunculo-pontine nuclei are spared. Diurnal fluctuation of symptoms is due to diurnal fluctuation of TH and DA at NS-DA terminal. Decreased DA to below 20% of normal, shown by polysomnographical studies, and its physiological age related decremental changes in NS-DA terminal underlies characteristic clinical course. High D2 receptor before early thirties masks D1 related hypertonus and manifest progression before 20 years of age. Other pteridine abnormalities also cause dopa responsive postural dystonia with diurnal fluctuation. A case of juvenile parkinsonism without dystonia showed decreased TH in dorsolateral putamen where indirect pathway is predominant. These suggest that decreased TH due to decreased BH4 involves D1-direct pathway causing dystonia, and decreased TH itself involves D2-indirect pathway causing parkinsonism.